Spiral Matrix.java

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

[
  [ 1, 2, 3 ],
  [ 4, 5, 6 ],
  [ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].


public class Solution {
    public ArrayList<Integer> spiralOrder(int[][] matrix) {
	ArrayList<Integer> list = new ArrayList<Integer>();
        if (matrix.length == 0) return list;
	int beginX = 0, endX = matrix.length - 1;
	int beginY = 0, endY = matrix[0].length - 1;
	while (true) {
	    for (int i = beginY; i <= endY; i++) {
		list.add(matrix[beginX][i]);
	    }
	    if (++beginX > endX) break;
	    for (int i = beginX; i <= endX; i++) {
		list.add(matrix[i][endY]);
	    }
	    if (beginY > --endY) break;
	    for (int i = endY; i >= beginY; i--) {
		list.add(matrix[endX][i]);
	    }
	    if (beginX > --endX) break;
	    for (int i = endX; i >= beginX; i--) {
		list.add(matrix[i][beginY]);
	    }
	    if (++beginY > endY) break;
	}
	return list;
    }
}